Semiconductor Properties of Recrystallized Silicon in Aluminum Alloy Junction Diodes

Abstract

This is a study of the basic electrical properties of thin recrystallized regions formed in the fabrication of PN junctions by the alloying of pure aluminum on N-type silicon single crystals. The average aluminum concentration is about 7×1018 cm−3, and varies by a factor of 4 to 5; being largest in the region first recrystallized and decreasing in a linear manner to the surface immediately beneath the aluminum-silicon eutectic. The average Hall-hole mobility is about 55 cm2 volt−1 sec−1 and varies from 35 to 75 cm2 volt−1 sec−1 across a region formed by precipating from 977°C to the eutectic. Across the same region the conductivity varies from 72 to 35 mho cm−1. The built-in field which is both a function of depth and total width can vary from 10 to 200 v per cm in typical cases. The minority carrier (electron) diffusion length ranges from 4 to 12 μ. The temperature dependence of the distribution coefficient corresponds to an enthalpy change (differential heat of solution) of +0.43 ev necessary for the transfer of an atom of aluminum from the liquid to the solid.